Single- to 3-phase transient phase conversion in induction motor drives

The paper analyses the requirements for transient phase balance when operating 3-phase induction motors from a single-phase supply. It is shown that exact phase balance can never be achieved with a single-capacitor phase convertor. The required parameters of a two-element phase convertor are determined as functions of motor slip. AC phase control and AC current chopping are used to maintain the convertor parameters at the required values. It is shown that balanced phase conversion can be achieved from standstill to full speed in a direct-on-line starting, cage induction motor drive. The system is capable of accelerating a loaded motor and of maintaining supply balance to the motor as the load changes.